Determining an endpoint in a polishing process

Abstract

In a polishing process (e.g. CMP), the endpoint is declared after (a) detecting that the friction between the polishing tool and the structure being polished is rising, then (b) determining that the friction is falling, then (c) waiting for a predetermined period of time (which can be zero). This algorithm results in reduced over-polishing in some embodiments. Other embodiments are also described.

What is claimed is:  
     
       1. A manufacturing method comprising: 
       (a) polishing a structure comprising a substrate and at least a first layer disposed above the substrate, to thereby remove at least a portion of the first layer;  
       (b) determining and declaring an endpoint for the polishing operation based on friction present between the structure and a polishing tool used for performing the polishing;  
       (c) stopping said polishing upon said declaring of the endpoint;  
       wherein said determining and declaring of the endpoint includes the following machine-implemented operations:  
       (b.1) first detecting that the friction has a friction versus time waveform with a first average slope indicating that the friction is steadily rising,  
       (b.2) second detecting, after said first detecting, that the friction versus time waveform has a second average slope indicating that the friction is steadily falling; and  
       (b.3) wherein said declaring of the endpoint occurs immediately after said second detecting or a predetermined amount of time after said second detecting.  
     
     
       2. The method of  claim 1  wherein said determining and declaring of the endpoint further includes the following machine-implemented operation: 
       (b.4) carrying out a third detecting between said second detecting that the friction is falling and said first detecting that the friction is rising, where the third detecting comprises detecting that the friction versus time waveform has a relatively flattened section indicating that the friction is neither steadily rising nor steadily falling for at least a predefined time period before the second detecting indicates the friction is steadily falling.  
     
     
       3. The method of  claim 1  wherein the machine-implemented operations of said first and second detectings are performed by a programmable circuit that is programmed to detect a local maxima of the friction versus time waveform. 
     
     
       4. The method of  claim 1  wherein said determining and declaring of the endpoint further includes the following machine-implemented operations: 
       (b.4) carrying out a third detecting between said first and second detectings, where the third detecting detects that that the friction versus time waveform has a third average slope indicating that the friction is steadily falling; and  
       (b.5) carrying out a fourth detecting between said third and second detectings, where the fourth detecting detects that that the friction versus time waveform has a fourth average slope indicating that the friction is steadily rising before the second detecting indicates the friction is steadily falling.  
     
     
       5. The method of  claim 1  wherein the substrate comprises an insulating layer, and the polishing continues until the insulating layer is exposed. 
     
     
       6. The method of  claim 5  wherein the first layer comprises a first sub-layer formed on the insulating layer and a second sub-layer formed over the first sub-layer, 
       wherein the first and second sub-layers have a substantially similar chemical compositions but at least one of respective, different densities and different surface roughnesses.  
     
     
       7. The method of  claim 6  wherein the second sub-layer has a lower density and a higher surface roughness than the first sub-layer. 
     
     
       8. The method of  claim 6  wherein each of the first and second sub-layers respectively comprises titanium or titanium nitride. 
     
     
       9. The method of  claim 5  wherein the first layer comprises: (1) a titanium nitride layer formed on the insulating layer, and (2) a conductive layer formed on the titanium nitride layer. 
     
     
       10. The method of  claim 9  wherein the titanium nitride layer is formed by physical vapor deposition (PVD). 
     
     
       11. The method of  claim 9  wherein at least a portion of the titanium nitride layer is formed by ionized PVD as the substrate is lying on a support biased with an AC bias of more than 150W. 
     
     
       12. The method of  claim 11  wherein the AC bias is at least 200 W. 
     
     
       13. The method of  claim 11  wherein the AC bias is at least 250 W. 
     
     
       14. The method of  claim 11  wherein the AC bias is at least 400 W. 
     
     
       15. The method of  claim 11  wherein the AC bias is 500 W. 
     
     
       16. The method of  claim 11  wherein the titanium nitride layer has a thickness of at least 8 nm. 
     
     
       17. The method of  claim 9  wherein the conductive layer comprises tungsten. 
     
     
       18. The method of  claim 1  wherein the substrate has a surface and an opening defined in said surface, the first layer is formed on the surface of the substrate and extending into the opening, and during the polishing, material of the first layer is removed from the surface of the substrate but not from the opening. 
     
     
       19. A device for controlling a polishing process of polishing a structure comprising a substrate and a first layer formed on the substrate, the device comprising circuitry for determining and declaring an endpoint for the polishing operation based on a signal indicative of friction between a polishing surface and the structure; 
       wherein said circuitry for determining and declaring the endpoint comprises:  
       (a) first means for detecting that a magnitude versus time waveform of the friction indicating signal has successive first and second waveform sections indicating that the friction is first, on average rising, and second that the friction is on average falling; and  
       (b) second means which is responsive to the first means and is programmable for declaring the endpoint immediately after the first means detects the second waveform section or a predetermined amount of time after the first means detects the second waveform section.  
     
     
       20. The control device of  claim 19  wherein the first means is part of a programmable device that is programmed to perform said detecting of the successive first and second waveform sections. 
     
     
       21. A machine implemented method for halting chemical mechanical polishing (CMP) of a workpiece having a sequence of layers, where the layers exhibit different frictions relative to a utilized CMP tool, the method comprising: 
       (a) receiving a friction-indicative signal which is indicative of friction between the workpiece and the CMP tool;  
       (b) first detecting that the friction-indicative signal has a magnitude versus time waveform with a first section whose average slope over a corresponding first duration indicates that the friction is on average, rising during the first duration of that first section of the waveform;  
       (c) second detecting that the magnitude versus time waveform has a second section, following the first section, where the average slope of the second section over a corresponding second duration indicates that the friction is on average, falling for that second section of the waveform; and  
       (d) in response to said first and second detectings, halting the chemical mechanical polishing a predetermined amount of time after said second detecting, where the predetermined amount of time is zero or greater than zero.  
     
     
       22. The machine implemented halting method of  claim 21  wherein: 
       said sequence of layers includes a layer of comparatively high density and a layer of substantially lesser density.  
     
     
       23. The machine implemented halting method of  claim 21  wherein: 
       said sequence of layers includes a layer having comparatively large surface roughness and a layer with a substantially smoother surface for presentation to the CMP tool.  
     
     
       24. The machine implemented halting method of  claim 21  wherein: 
       (b.1) said first detecting is validated by a continuous succession of UP windows through which the first section of the waveform extends.  
     
     
       25. The machine implemented halting method of  claim 24  wherein: 
       (c.1) said second detecting is validated by a continuous succession of DOWN windows through which the second section of the waveform extends.  
     
     
       26. The machine implemented halting method of  claim 24  wherein: 
       said sequence of layers includes a titanium nitride layer.  
     
     
       27. The machine implemented halting method of  claim 21  wherein: 
       (d.1) said predetermined amount of time is greater than zero but terminates before the friction-indicative signal flattens out after the second section of the waveform.